Tone receiver for undamped oscillations



Nov. 6, 1928; 1,690,918

J. ZENNECK ET AL TONE RECEIVE-R FOR mm OSCILLATIONS Filed April 28, Y 1923'- 2 Sheets-Sheet 1 Z bi.

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W BY a %w gA mg Nov. 6, 1928. 1,690,918

J. ZENNECK ET AL TONE RECEIVER FOR UNDANPED OSCILLATIONS I Filed April 28, 1923 2 Sheets-Sheet 2 A MTTORNES Patented Nov. 6, 1928.

UNITED ST S PATENTTOFFICE.

JONATHAN ZENNECK, OF MUNICH, GERMANY, Ania nnsr KNOPP, or NEWY-Y'ORK, N, Y.

TONE RECEIVER FOR UNnAMrEn OSCILLATIONS.

Application filed April 28, 1923. Serial No. 635,311.

Our invention relates to the reception of undamped'waves such as arev use in radio telegraphy, and it is the particular purpose of this invention to receive such waves or signals which are'sent by means of such waves, in the form of audible tones in an aural receiver, for instance a telephone.

The fundamental idea on which our invention is based consists in producing in'the system by which the arriving undamped oscillations are received, damped oscillations at regular intervals and a suitable number of. times per second, which damped oscillations are superimposed upon the received undamped oscillations. These damped oscilla- I tions may be produced. in the form of impulses imparted to an oscillatory circuit which is part of th'ereceiving system,by any suitable means known in the art. The oscillations resulting from such a superimposh tion of aforesaid impulses upon the received undamped oscillations are oscillations of a periodically varying amplitude. If now a detector circuit is suitably coupled with the circuit carrying these periodically varying oscillations, one or several tones are obtained which correspond withthe periodical variations of the amplitude of the resulting os-' cillations. j I

Theamplitude of the above-mentioned resulting oscillations depends upon the. condition of the phase ,of the received undamped oscillations, at which theimpulse excited oscillationsstart; vThus a regular periodical variationof thisamplitude'can only occur if the-difference between the. individual in tervals within which the impulse occurs, is very'small comparedwith the high frequency period of the received undamped oscillations.- I

If this condition is fulfilled generally a double tone will be received in the detector circuit, both of which tones are of a frequency which is different from the frequency at which the impulses occur. Only at a very definite relation between the high frequency of the received oscillationsand the impulse frequency, the two resulting tone frequencies will coincide so that only one tone will be heard in the telephone connected into the detector circuit.

It would be very difficult to produce impulses. of such a regularity as is required for the productionof a musical 'tone-inthe tele phone by mechanical means, i.; e. by mechani cal interrupters. We have found, however, that thermionic relays are very well suited for producing impulses'of a desired low frequency Which are adapted to impart the necessary impulses to a local high frequency circuit at absolutely regular intervals. Of

course, the degree of regularity depends upon keeping the plate voltage and the fila nient current constant; i

"The circuit arrangements which may be used for locally producingsuch a low frequencyforthese impulse purposes may Vary considerably since at the present day quite a number of different circuit connections for thermionic relays are known in the art by which such relays are'caused to produce continuous oscillations of any desired frequency- In the accompanying drawings we have illustrated several circuit arrangements in which the idea involvedin our invention may be reduced to practice withoutthereby limiting the practical form of our inventionto these modifications shown, since it is obvious to any one skilled in the art that similar results may be obtained by varying the individual detailsof the elements "of which the circuit arrangement is composed.

Referring to these drawings Figures 1, 2 and 4 represent modified forms of circuit diagrams by which the effect referred to 'hereinbefore may be obtained;

and 1 1 3 t l" ll llle iepresen s a curve clagram which will be explained hereinafter.

Referring now in detail to Figure 1, A,

represents an antenna by whichforexample.

the undamped waves may be received. The

circuit G, L L L represents a local high frequency oscillatory circuit in "which it is lTJIOPOSEECL'QCCOICllHg to thepresent inven tion, to produce damped oscillations by regularly occurring impulses. -This local oscil' lating circuit is shown in the diagram bv .heavy lines and it is coupled at L with the art. The relay circuits consist of the plate circuit containlng the plate P, the battery B and the filament F and besides a suitable number of choking coils D D and of the grid circuit including the grid G, a grid potential battery E transformer coil S and the filament F. The filament is heated by means of the heating battery H Whose curren is controlled by means of the rhcostat R. lathe modification shown as an example the low frequency impulsecircuit is conductively. coupled with the local high frequency circuit by the connection with the circuit at either side of condenser C.

The detector circuit is represented by the circuit C L and coupled at L with the inductance L of the local high frequency circuit The dectector l) is connected to the detector circuit in the conventional manner known in the art and includes 1L? connections a blocking condenser C" and a telephone T. The detector D is illustrated onlyby the conventional symbol f r detectors and may represent any suit:

such for instance an elec tector,, a crystal detector, an os ill t non-oscillating audion or the use, which expedients are Well known in the art.

If now for instance in the arrangement according to'l igure 1 the condensers C and C are adjustcd such that the tone intensity in the telephone is quite satisfactory and if new the low impulse frequency is gradually increased for instance by varying the condenser C the follorvving phenomenon occurs which is represented in the curve diagram Figure 3: at a certain low impulse frequency N, a singletons is produced Whose frequency is equal to the impulse frequency N. If now the loW impulse frequency is gradually further increased, two tones Wlll is produced, the pitch of one of Which he comes higherand higher Whereas the pitch of the other becomes lower and lower and finally the latter tone becomes inaudible. From a certain value of the gradually in creased impulse frequency, namely the value N in Figure 8 the pitch of the higher tone commences gradually to decrease, Whereas the pitch of the lower tone again increases until both tones again coincide at a value N On further increasing the impulse frequency the same phenomenon occurs, Whereby the maximum pitch of the higher tone becomes higher with each progressing cycle asis indicates by the dotted line 2N.

The pitch of the tone is practically independent of the adjustment of the condenser U and thus of the frequency of the local high irequency circuit shown in heavy lines. A variation of the condenser C either does not vary the tone at all or to only a very slight and immaterial extent. In case it should circuit slightly vary it can easily be proven that such a slight variation of the tone-is caused by the fact that by varying the capacity of condenser C a slight influence is exerted upon the f quency of the impulse frequency circuit. On the other hand, by variation of condense 1" C the tone intensity of the resulting tone is varied to a considerableqeutent, This intensity is a n'iarliinum for a certain capacity Value of condenser C and decreases, the variation ct condenser C in either direction from this resonance adjustniient, in the form of resonance curve. V

The phenomenon illustrated in the curve diagram Figure 3 might be explained as follows? 7 V i The fundamental impulse frequency produced in the low frequency circuit has higher harmonics, some of which have freprencies in the vicinity of the received high frequencies. These. harmonics are transferred into the local high frequency oscillation circuit, where they formbeats. With the received frequency, 7 which beats are audible in the telephone. The double tone produced by beats Withthe two harmonics to the received frequency. If'the received frequency is located exactlyin the middle between two adjacent harmonics, the two beat frequenciesproduced are identical and thus only one tone will he audible. This is also the case if the received frequency and one of the harmonics are identical in frequency. If on the other hand the received frequency is not located in the middle, the beat frequency produced with one of the harmonics: will be'diflierent from the beat frequency produced with the other harmonic'and a double tone will result.

Figure 2' is distinguished from Figural only by the feature that in Figure 2 not only the impulse frequency circuit 6,, 19 but also the local high frequency circuit L L L is coupledwith the grid circuit of the thermionic relay by means of a coupling coil L. The result of such an additional coupling is that in the local high frequency circuit, damped high frequency oscillations: are produced Witha varying amplitude even if no undam-ped high frequency oscillations arrive at the antenna. The advantage of such an arrangement is that the tone intensity in the telephone becomes by far greater.

his arrangement, however, has the disadvantage th at the adjustment of the different variable elements in order to produce a good tone is very sensitive and critical. The probable reason for this sensitiveness is that disturbing heattones. may be produced.

In both modifications Figures: 12 and d it is essentialfor the production of a good tone and a good etficiency to correctly adjustthe heating current'and the plate voltage of the thermionic relay. 1 t Y a high frequency circuit may each be individually coupled with the detector circuit by means of the inductances L and L without changing the result described. The characteristic features by which our invention is distinguished over devices heretofore used 7 a for receiving undamped oscillations in the form of audible tones are as follows Firstly the tone which is produced in the receiving telephone is in its'frequency different from the frequency of the low frequency' impulse circuit C p, except in the particular cases described hereinbefore with reference to Figure 3. Our arrangement is thus clearly distinguished from the arrangements involving so-called tone superimposition known to the present day art in which a local undamped low frequency is superimposed directly upon the received undamped high frequency, which arrangement is shown and described for instance in U; S.

Secondly the harmonics produced in the local high frequency circuit C L L L are produced by a local low frequency source and 1 permit the convenient reception with two tones, whereas the ordinary 'heterod ne' method with its single tone renders it o n difiicult to hold the transmitting station in the receiving telephone.

We claim In an arrangement for receiving and'detecting undamped high frequency oscillations, the combination of av receiving circuit patentof Alexander Meissner No. 1,170,552. 7

for receiving said undamped high frequency oscillations, a local high frequency oscillating circuit associated therewith, anda local low frequency impulse generator circuit coupled with said local high frequency oscillating circuit, and a detector circuit suitably connected to receive the resulting oscillations produced in said local high frequency oscillating circuit and including an aural receiver for producing audible tones from the received high frequency current and the adjacent harmonics of the superimposed'low frequency current.

JONATHAN ZENNECK. 7

- ERNST KNOPP. 

